Electrically-heated pad



Se t. 15, 1925. 1,553,868

J. A. M DONALD ELECTRI CALI-Y HEATED PAD Filed Jan. 10, 1925 'INVEINTUR.

Jazz M w w- Patented Sept. 15, 1925.

UNITED STATES PATENT oFF1cE.

JAMES ALEXANDER MACDONALD, OF BBAN TFORD, ONTARIO, CANADA.

ELECTR-ICALLY-HEATED PAID. 1

Application filed January 10, 1925. Serial No. 1,705.

This invention relates to electrically heat ed pads of the type which are commonly 1 used in place of hot water bottles. as well as for a variety of other purposes, and which consists of a heating element which is secured between two plies offabric or other material. The heating elements are usually arranged so as to give any one of three heats, full, medium or low. These elements as a rule are fairly satisfactory when operating on full heat, but when it is desired to operate on medium or low heat the elements as heretofore arranged are objectionable in that the heat is unevenly distributed, that is'to say, parts of the pad will be highly heated while other parts will be comparatively cool. e

The object of my invention'therefore is to devise a pad which will be more evenly heated over its whole surface when the element is operating at medium or low heat, and thus avoid the formatior. of hot and cool spots as hereinbefore referred to. Many of the constructions now on the market, while quite flexible, have a marked tendency to fly back to the flat position when released, and a further object of the present invention, therefore, is to devise a pad which will more readily remain in any shape into which it may be bent;

A still further object is to construct the pad in order that the life of the resistance wires maybe increased.

I attain my objects by means of the constructions hereinafter described and illustrated in-the accompanying drawing which is a plan view of my improved pad, partially "broken away. The pad consists of an envelope comprising a back 1 and front 2 of any suitable material suitably secured together at their edges. Within the envelope is placed the heating element, and it is in the arrangement of this element that the present invention is particularly concerned.

The element comprises two wires 3 and 4, each being enclosed in a tubular covering of asbestos or other insulating material.

in one direction while the parts The passage through the tubular covering is of somewhat greater size than the wire, so as to give the latter plenty of room for expansion. The wire 3, it will be noted, is doubled back and forth on itself so that it runs mainly in a direction longitudinally of the pad, while the wire 4 is doubled back and forth on itself so that it runs mainly in a direction transvorselyof the pad. One end of the wire 3 ed with the lead \vire 6, while the other end of each wire is connected with a wire. 10, which leads to one terminal of a thermostat 9. A third lead wire 7 is connected to the other terminal of the thermostat by means of which the circuit may be broken when the temperature of the pad reaches a certainheight 1 and closed when the temperature of the pad is reduced to a sufficient extent.

The wires 3 and 4, while they may be secured in the desired position relative to one another in any convenient manner, are preferably loosely interwoven to form in effect a fabric, sufficient air ventilating; space be- 'ing left between. the strands to allow for quick drying out of any moisture which may be absorbed by the pad. This is of km portance as many pads have broken down through the absorption of moisture and the failure to provide ing the time the padis drying out.

is connected with a lead' wire 5 while one end of the wire 4 is connect.

sufficient ventilation dur- The lead wires 5, 6, and 7 are all led to i a three-way switch 8 of any ordinary type, so that either or both the wires 3 and 4 may be supplied with current, depending on whether it is desired to heat the medium or high temperature.

The total capacity of the pad will usually be sixty watts, one element being 35 watt capacity and the other 25, both elements pad to low,

being in parallelat high heat, the 35 watt element in use at medium heat and the 25 watt element at low heat.

It will be seen from the construction illustrated and described that when current is cut off from one of the element wires, the other element wire is so arranged that there are no large spaces on the face of the pad which are not supplied with heat.

What I claim is:

1. In an electrically heated pad, a heating element comprising two independent circuits, the parts of one circuit lying mainly of the other circuit lie mainly in a direction at an angle to the direction in which the parts of the first mentioned circuit mainly lie.

2. In an electrically heated pad, a heatin element comprising a pair of insulated resistance wires, one wire being doubled back and forth on itself so that it lies mainly in one direction, while the other wire is doubled back and forth on itself so that it lies. mainly in a direction at an angle to the-direction of the first mentioned Wire.

3. In an electrically heated pad, a heating element comprising a pair of insulated resistance wires, one wire being doubled back and forth on itself so that it lies mainly in a direction longitudinally of the pad, while the other wire is doubled back and forth on itself so that it lies mainly transversely of the pad.

4. In an electrically heated pad, a heating element comprising a pair of insulated resistance wires, one wire being doubled back and forth on itself so that it lies mainly in one direction while the other wire is doubled back and forth on itself so that it lies mainly in a direction at an angle to the direction of the first mentioned wire, said wires being interwoven to retain them in their relative position.

5. In an electrically heated ad, a heating element comprising a pair 0 insulated resistance wires, one wire being doubled back and forth on itself so that it lies mainly in a direction longitudinally of the pad, while the other wire is doubled back and forth on itself so that it lies mainly transversely of the pad, said wires being interwoven to retain them in their relative position.

' 6. In an electrically heated pad, a heating element comprising a pair of resistance wires, one Wire being doubled back and forth on itself so that it lies mainly in one direction, while the other wire is doubled back and forth on itself so that it lies mainly in a direction at an angle to the direction of the firstmentioned wire, said wires being enclosed inloosely fitting insulating tubing.

7. In an electrically heated pad, a heating element comprising a pair of resistance, wires, one Wire being doubled back and forth on itself so that it lies mainly in one direction, while the other wire is doubled. back and forth on itself so that it lies mainly in a direction at an angle to 'the direction of the first mentioned wire, said wires being enclosed in loosely fitting asbestos tubing.

8. In an electrically heated pad, a heating element comprising a pair of insulated re sistance wires, one wire being doubled back and forth on itself so that it lies mainly in one direction while the other wire is doubled back and forth on itself so that it lies mainly in a direction at an angle to the direction of the first 'mentioned Wire, said wires being loosely interwoven to retain them in their relative position.

Signed at Brantford, Canada, this 19 day of December, 1924.

JAMES ALEXANDER MAoDONALD. 

